Lawmakers in Niagara Falls, N.Y., are asking for a criminal investigation into the discharge of inky, foul-smelling wastewater that turned the water below Niagara Falls black.

The Niagara County legislature passed resolutions Thursday night that request investigations by the New York state attorney general, the Niagara County district attorney and the federal Environmental Protection Agency.

The legislators want the agencies to investigate the July 29 discharge that turned the water near the base of the falls black on a sunny day when the area was crowded with tourists.

The Niagara Falls Water Board says workers at the local wastewater treatment plant let a pump run for too long while emptying a sedimentation basin. The basin contained residue from the cleaning of carbon filters at the plant.

Several state legislators have asked for their attorney general, the district attorney and the Environmental Protection Agency to investigate. Niagara Falls MPP Wayne Gates has also called for an investigation in an open letter to provincial Environment Minister Chris Ballard.

If found guilty of violating state water quality standards, the city could face a fine of up to $37,500. 

When it appeared, the inky water enveloped the dock for the popular Maid of the Mist tour boats.

Officials say the blackish water contained accumulated solids and carbon residue but no organic oils or solvents. They described the odour as "normal sewer water discharge smell."

The water board says the discharge was within permitted limits.